This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-402001, filed on Dec. 28, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electrostatic actuator and a camera module which are driven by an electrostatic force, more specifically to those capable of maintaining actuator performance without reference to temperature variations.
2. Description of the Related Art
An electrostatic actuator includes a movable element, and a substantially-rectangular stationary element that defines a space extending in a predetermined direction and allowing the movable element to move therethrough. The gap between the movable element and the stationary element is of the order of several microns. The movable element has a pair of surfaces that face the inner walls of the stationary element, and a convex stripe electrode is formed on each of those surfaces, thereby forming electrode surfaces. The stationary element has electrode plates on which electrodes are formed. The electrodes are formed at positions facing the electrode surfaces of the movable element. In the electrostatic actuator having this structure, the movable element is electrostatically driven when the electrodes of the stationary element are applied with voltage in a predetermined order.
The stationary element of the electrostatic actuator is formed by disposing the electrode plates in a mold and then inserting resin or the like into the mold. The movable element is formed likewise. This formation method is generally used since it is advantageous in terms of the manufacturing cost and suitable for mass production.
An electrostatic actuator whose movable element and stationary element are formed in the above resin-insertion method has the following problems. In order for the electrostatic actuator to attain its desired driving power, the gap between the movable element and the stationary element must be determined and maintained with high precision. When the resin-insertion method is used, however, the dimensions of movable elements and stationary elements vary greatly, so that high precision is hard to attain. This gives rise to variations in the actuator performance. Furthermore, the wiring portions of the electrode plates are exposed to high pressure and high temperature at the time of resin insertion. Since the wiring portions are likely to break, the manufacturing yield may deteriorate.
An object of the present invention is to provide an electrostatic actuator and a camera module which are formed with high precision and can therefore ensure desired actuator performance.
To solve the above problems and achieve the object, an electrostatic actuator according to the first aspect of the present invention comprises: a stationary element; and a movable element which is reciprocated in a predetermined direction while being guided by the stationary element and which is provided with a pair of opposing surfaces having electrodes thereon. The stationary element comprises: a pair of side members that face each other, with the moving space of the movable element being located therebetween; and a pair of electrode plates which face each other, with the moving space of the movable element being located therebetween, and on which electrodes are arranged in such a manner as to oppose the electrodes of the movable element. One of the paired electrode plates has side surfaces that are in partial contact with inner walls of the side members opposing the movable element. The other one of the paired electrode plates is disposed in such a manner that its electrode surface is in partial contact with the side surfaces of the paired side members. The one of the paired electrode plates and the side surfaces of the side members are coupled together by use of an adhesive that is applied to the side surface of the one of the paired electrode plate and to the side surfaces of the side members. The other one of the paired electrode plates and the side members are coupled together by use of an adhesive that is applied to the side surface of the other one of the paired electrode plates and the side surfaces of the side members.
An electrostatic actuator according to the second aspect of the present invention comprises: a stationary element; and a movable element which is reciprocated in a predetermined direction while being guided by the stationary element and which is provided with a pair of opposing surfaces having electrodes thereon. The stationary element comprises: a pair of side members that face each other, with the moving space of the movable element being located therebetween; and a pair of electrode plates which face each other, with the moving space of the movable element being located therebetween, and on which electrodes are arranged in such a manner as to oppose the electrodes of the movable element. The paired electrode plates have side surfaces that are in partial contact with inner walls of the side members. The paired electrode plates and the paired side members are coupled together by use of an adhesive that is applied to the side surfaces of the paired electrode plates and to the side surfaces of the side members.
An electrostatic actuator according to the third aspect of the present invention comprises: a stationary element; and a movable element which is reciprocated in a predetermined direction while being guided by the stationary element and which is provided with a pair of opposing surfaces having electrodes thereon. The stationary element comprises: a pair of side members that face each other, with the moving space of the movable element being located therebetween; and a pair of electrode plates which face each other, with the moving space of the movable element being located therebetween, and on which electrodes are arranged in such a manner as to oppose the electrodes of the movable element. The paired electrode plates have side surfaces that are in contact with inner walls of the side members. The paired electrode plates and the paired side members are coupled together by use of an adhesive that is applied to the electrode surface of one of the paired electrode plates and to inner side surfaces of the paired side members and by use of an adhesive that is applied to the reverse surface of the other one of the paired electrode plates and to the inner wall surfaces of the paired side members.